The invention relates to a variable valve control for a piston internal combustion engine with at least one inlet valve and at least one outlet valve, an inlet-outlet camshaft including an inlet valve opening cam for controlling the opening time of the inlet valve, an outlet cam for operating the outlet valve, an inlet valve closing camshaft having an inlet valve closing cam for controlling the closing time of the inlet valve, an inlet valve operating lever for transferring the control motion of the inlet valve opening cam and of the inlet valve closing cam to the inlet valve, an outlet valve operating lever for transmitting the control motion of the outlet valve operating cam to the outlet valve and a device for changing the phase relationship between the two camshafts.
Such an arrangement is known, for example, from DE 196 00 536 A1. The arrangement permits the reduction of exhaust gas emissions and also an increase of the engine torque. By reducing the energy needed for the gas exchange the fuel consumption of the engine can also be reduced. Furthermore, there is no need for a throttle valve in the intake duct of the engine.
The arrangement comprises two camshafts, one including an inlet cam for controlling the opening functions of the inlet valve and an exhaust cam for controlling the exhaust valve. The other camshaft includes an inlet valve closing cam for controlling the closing time of the inlet valve. The inlet valve opening and closing cams act in an additive fashion and together determine the opening lift and opening duration of the inlet valve. With a device for changing the phase relation between the two camshafts, the relative angle between the two camshafts can be controlled in order to adjust the opening lift and opening duration of the inlet valve.
The inlet valve opening cam and the inlet valve closing cam are disposed in a common plane so that the rotation of the inlet valve opening cam on the first cam shaft and the rotation of the inlet valve closing cam on the second cam shaft occur in the same plane of movement. Although such a serial arrangement of the inlet cams requires only a small installation space, the exhaust cam, which is arranged on the side of the inlet valve opening cam is displaced axially from the exhaust valve which requires the use of an offset valve opening lever: the contact point between the exhaust cam and the exhaust valve operating lever is disposed outside the center plane of the exhaust valve, that is, outside a plane extending normal to the camshaft and through the exhaust valve axis. This asymmetrical arrangement generates bending forces, which accelerate wear and detrimentally affect precise motion transmission between the cam and the valve.
Furthermore, arrangements for a variable valve control are known which include two inlet valve opening cams and two outlet valve operating cams. The inlet valve opening cam on the one cam shaft is spaced from the inlet valve closing cam on the other cam shaft and the outlet valve operating cams are disposed at axially opposite sides of the inlet valve opening cam. But in this arrangement, the control motion of the exhaust cams must also be transmitted to the exhaust valve by an offset operating lever. In addition, the arrangement of four cams in side-by-side relationship on one camshaft requires a relatively large amount of space so that adjacent cylinders must be relatively widely spaced and the engine becomes relatively long.
It is the principal object of the present invention to provide a variable valve control for an internal combustion engine, which requires relatively little space, but has a high operational reliability.